A TDMA-based or CDMA/TDD-based mobile communication specifies a slot, which is an arbitrary unit time, assigns a user to each slot and switches between transmission and reception for every frame, which consists of a plurality of slots.
A conventional transmission/reception apparatus provided on a base station apparatus and communication terminal apparatus will be explained below using FIG. 1. FIG. 1 is a main block diagram showing an outlined configuration of a conventional transmission/reception apparatus.
Here, the present application relates to transmission timing control and its processing is mainly performed by a control signal, and therefore detailed explanations of user data and its processing system will be omitted in the following explanations and drawings.
In the transmission/reception apparatus shown in FIG. 1, antenna 1 transmits/receives a radio signal, duplexer 2 switches between input and output of a transmission/reception signal to/from antenna 1 and reception RF section 3 performs reception processing on a reception signal.
Matched filter (hereinafter referred to as “MF”) 4 calculates a correlation value in a known symbol interval of the reception signal using a preset known symbol, detects a channel estimated value of the reception signal and outputs the channel estimated value to demodulation section 6, which will be described later. Sliding correlator (hereinafter referred to as “SC”) 5 performs despreading processing on the reception signal using an intrinsic code.
Demodulation section 6 performs a complex multiplication on the channel estimated value for each despread reception signal, compensates phase rotation and amplitude variation and demodulates. CRC check section 7 decides whether demodulation is performed on the demodulated reception signal correctly or not.
Modulation section 8 performs modulation on the decision result, which is the output of CRC check section 7, that is, the decision result as to whether reception has been performed correctly or not, and transmission RF section 9 performs transmission processing on the decision result subjected to modulation processing and transmits the decision result from antenna 1 via duplexer 2.
This transmitted decision result is, in other words, a retransmission request and the other end of communication which receives this signal continues transmission if the decision result of the reception condition shows that reception has been acceptable with no error and retransmits a transmission signal if the decision result shows that reception includes some errors and has not been performed correctly.
As shown above, based on the decision result after demodulation processing, the conventional transmission/reception apparatus sends a retransmission request to the other end of communication in the case where reception has not been performed correctly.
Next, the method of extracting data of each user assigned to each slot based on a TDMA or CDMA/TDD system will be explained using FIG. 2. FIG. 2 is a schematic diagram showing how slot reception is performed in the conventional transmission/reception apparatus.
In the case where the conventional transmission/reception apparatus is used for a communication terminal apparatus, each data piece is extracted as shown in FIG. 2, by the reception system operating only in a desired data interval and turning off in data intervals for other users.
Moreover, in the case where the conventional transmission/reception apparatus is used for a base station apparatus carrying out a radio communication with a plurality of communication terminal apparatuses, the transmission/reception apparatus receives a radio signal from each user by changing the reception interval for every user.
Here, each slot is normally provided with guard times containing no data so that reception is possible within the reception interval even if a delay is produced in the reception signal.
That is, a reception interval has a length adding up the user data length and the guard time length and the guard time serves as a margin interval in the case where a delay is produced in the reception signal.
Therefore, even if a propagation delay is produced in the reception signal, the entire slot can fit in the reception interval as long as the delay time is within the guard time length, and therefore the entire slot is received correctly.
However, in the case where a delay exceeding the guard time length is produced, the conventional transmission/reception apparatus has a problem of being unable to receive data after the reception interval. A more detailed explanation will be given below with reference to FIG. 3. FIG. 3 is a schematic diagram showing slot reception in the conventional transmission/reception apparatus.
FIG. 3A shows a case where the delay time is shorter than the guard time length and, as shown in the figure, the one entire slot fits in the reception interval and all data is received.
On the other hand, FIG. 3B shows a case where the delay time is longer than the guard time length and the rear end of the data symbol does not fin in the reception interval, preventing the area beyond the reception interval from being received.
When a CRC check detects that reception has not been performed correctly, as already explained using FIG. 3, a retransmission request is sent to the other end of communication, which is the transmission source.
However, in the case where this delay is considered attributable to a long distance between the communication stations, this propagation delay is considered to continue almost constantly, repeating retransmission requests; hence the problem of being unable to continue communications indefinitely.